CO2分压对碳钢海底管道CO2/H2S腐蚀的影响

目的：研究 CO2分压对 CO2/H2S腐蚀的影响规律，为海底管道材料的选择提供参考依据。方法采用高温高压反应釜进行腐蚀模拟实验，对腐蚀前后的试样进行称量，计算腐蚀速率。通过SEM观察腐蚀产物膜形貌，通过 XRD 分析腐蚀产物膜成分。结果当 CO2/H2S 分压比较高（1200）时， CO2分压为0.3、0.5、1.0 MPa对应的腐蚀速率分别为1.87、3.22、5.35 mm/a，随着CO2分压升高，腐蚀速率几乎呈线性增大趋势。当CO2/H2S分压比较低（200）时，CO2分压为0.3、0.5、1.0 MPa对应的腐蚀速率分别为3.47、3.64、3.71 mm/a，CO2分压变化对腐蚀速率的影响并不显著。当CO2/H2S分压比较高（1200）时，腐蚀产物以FeCO3为主，腐蚀受CO2控制；此时低CO2分压下的腐蚀产物膜较完整致密，高CO2分压下的腐蚀产物膜局部容易破裂，对基体保护性下降，因此腐蚀速率随CO2分压升高而增大。当CO2/H2S分压比较低（200）时，腐蚀产物以FeS为主，腐蚀受H2S控制；此时在不同CO2分压条件下，腐蚀产物均较完整致密，因此腐蚀速率相对较低，并未随着CO2分压升高显著增大。结论 CO2分压对CO2/H2S腐蚀速率的影响与CO2/H2S分压比密切相关，海底管道材料选择不仅要考虑CO2分压的影响，还要考虑CO2/H2S分压比的影响。

Effect of Partial Pressure of CO2 on Corrosion of Carbon Steel Subsea Pipeline in CO2/H2S Environment

Objective To study the effect of partial pressure of CO2 on the corrosion in CO2/H2S environment, in order to guide the material selection of subsea pipeline. Methods Corrosion simulation test was carried out in the high-pressure high-temperature autoclave, the weight of the specimen was tested before and after corrosion simulation experiment, then the corrosion rate was calculated, and the morphologies and chemical composition of corrosion product scales were characterized by SEM and XRD. Results When the ratio of CO2/H2S was high (1200), at the partial pressure of CO2 of 0.3 MPa, 0.5 MPa, 1.0 MPa, the corrosion rates were 1.87 mm/a, 3.22 mm/a, 5.35 mm/a, respectively, and the corrosion rate increased almost linearly with the increase of CO2 partial pressure. When the ratio of CO2/H2S was low (200), at the partial pressure of CO2 of 0.3 MPa, 0.5 MPa, 1.0 MPa, the corrosion rates were 3.47 mm/a, 3.64 mm/a, 3.71 mm/a, and the influence of CO2 partial pressure on corrosion rate was not significant. When the ratio of CO2/H2S was high (1200), the main chemical composition of corrosion product scale was FeCO3, the corrosion was controlled by CO2; the corrosion product scale was compact under low partial pressure of CO2, the scale was easy to be ruptured, and the protection of the substrate was decreased, so the corrosion rate increased with the increase of partial pressure of CO2. When the ratio of CO2/H2S was low (200), the main chemical composition of corrosion product scale was FeS, the corrosion was controlled by H2S; the corrosion product scale was compact under different partial pressure of CO2, so the corrosion rate was relatively low, and there was no significant increase with the increase of partial pressure of CO2. Conclusion the effect of partial pressure of CO2 on the corrosion in CO2/H2S Environment was closely related to the ratio of CO2/H2S. We need to consider the effects of partial pressure of CO2 and the ratio of CO2/H2S on corrosion when we select materials for subsea pipeline.